1. Field of the Invention
The present invention relates to a pulse width modulation (PWM) circuit apparatus for converting analog signals to pulse widths (time widths).
2. Description of the Prior Art
A majority of conventional PWM circuits are known to contain a comparator, as illustrated in FIG. 1. In the circuit of FIG. 1, the non-inverting (+) and inverting (-) input terminals of the comparator 1 are fed with a sine wave voltage e.sub.i+ and a triangular wave voltage e.sub.i-, respectively.
Suppose that the frequency of the triangular wave is sufficiently higher than that of the sine wave and that the amplitude of the triangular wave is greater than that of the sine wave. In that case, the output voltage e.sub.0 of a comparator 1 takes on the waveform such as one contained in the timing chart of FIG. 2. As indicated, the period during which the output voltage e.sub.0 is High, i.e., the pulse width .tau. of the e.sub.0 output, is in proportion to the magnitude of the sine wave voltage e.sub.i+.
One disadvantage of the prior art PWM circuit apparatus utilizing the triangular wave voltage is that because of the inherent constraints on the precision of vertexes and on the linearity of inclinations associated with the triangular wave, there necessarily exist limits to improving the input level vs. pulse width characteristic in terms of linearity.